Electrostatic information recording medium

ABSTRACT

The electrostatic information recording medium of the present invention has an electric charge retaining layer 11 stacked on at least an electrode layer 13, as shown in FIG. 1. The electric charge retaining layer is formed from either 1 a resin selected from among fluorocarbon resins, and an insulating organic substance having no photoconductivity, or 2 a fluorine-containing thermoplastic resin consisting of a repeating unit represented by formula (1): ##STR1## (where the content of the dioxonol component represented by the number m of repeating units is in the range of 20 mol % to 90 mol %) 
     the fluorine-containing thermoplastic resin having a melt viscosity of 10 2  to 10 4  Pa.sec at a temperature which is 90° C. to 110° C. higher than its glass transition temperature.

This is a divisional of application Ser. No. 08/075,581 filed on Oct.25. 1993, now U.S. Pat. No. 5,527,589. International ApplicationPCT/JP92/01336 filed on Oct. 15, 1992 and which designated the U.S.

TECHNICAL FIELD

The present invention relates to an electrostatic information recordingmedium which enables information to be recorded thereonelectrostatically by, for example, a method wherein exposure is effectedunder application of a voltage, and which also permits the recordedinformation to be reproduced at any desired time. More particularly, thepresent invention relates to an electrostatic information recordingmedium which has excellent negative electric charge retainingcharacteristics and which is particularly excellent in positive electriccharge retaining characteristics and also superior in heat resistance,moisture resistance and processability.

BACKGROUND ART

There has heretofore been a known electrophotographic technique in whicha photoconductive layer deposited on an electrode layer is fully chargedand then subjected to image exposure, and the electric charge in theexposed regions is leaked, thereby optically forming an electrostaticlatent image on the photoconductive layer, and thereafter toner havingelectric charge which is opposite in polarity to the residual electriccharge is allowed to adhere thereto, thereby developing the image onpaper or the like by electrostatic transfer. This technique is mainlyemployed for copying purposes. The electrostatic charge retaining periodin the photoconductive layer as a recording medium is short, and tonerdevelopment is carried out immediately after the formation of anelectrostatic latent image. This technique cannot be used for otherpurposes, for example, photographing, because of low sensitivity.

In the meantime, an electrostatic information recording method byexposure carried out under voltage application has been developed inwhich an electrostatic information recording medium is disposedface-to-face with a photosensitive member having a photoconductive layerprovided on an electrode, and image exposure is carried out with avoltage being applied between the respective electrodes of thephotosensitive member and the recording medium, thereby recording anelectrostatic latent image of extremely high resolution on theelectrostatic information recording medium. It is extremely importantthat the electrostatic information recording medium used in thiselectrostatic information recording method should have excellentelectric charge retaining characteristics.

As resins used to form an electric charge retaining layer, fluorocarbonresins are superior in electric charge retaining characteristics butunfavorable in terms of processability required therefor when layered onthe electrode. As insulating materials, fluorocarbon resins exhibit highinsulation properties with respect to electrons. However, in the case oftetrafluoroethylene-hexafluoropropylene copolymer (FEP), for example,the mobility of electrons is not higher than 10⁻¹⁷ cm² /V.s, whereas themobility of holes is as high as 2×10⁻⁹ cm² /V.s. Thus, the insulationproperties with respect to holes cannot be said to be satisfactory.

On the other hand, polystyrene resins are superior in that the glasstransition temperature is-high and the moisture absorption is low.However, the electric charge retaining characteristics of these resinsare so low that none of them can be used as a material for an electriccharge retaining layer.

It is an object of the present invention to provide an electrostaticinformation recording medium having an electric charge retaining layerwhich is excellent in electric charge retaining characteristics,particularly in positive electric charge retaining performance, and alsoexcellent in heat resistance, moisture resistance and processability.

DISCLOSURE OF THE INVENTION

A first electrostatic information recording medium of the presentinvention is characterized in that an electric charge retaining layer isstacked on at least an electrode layer, and that the electric chargeretaining layer comprises a resin selected from among fluorocarbonresins and polystyrene resins, and an insulating organic substancehaving no photoconductivity.

The electrostatic information recording medium is further characterizedin that a spectrum of thermally stimulated currents, which is obtainedby measuring the electric charge retaining layer with an open-circuitthermally stimulated current measuring device after the electric chargeretaining layer has been positively charged, has a hetero-peak inaddition to a homo-peak.

In general, fluorocarbon resins have a high resistivity and a low waterabsorption, i.e., 0.01% or less, and exhibit excellent moistureresistance irrespective of whether the retained electric charge ispositive or negative and hence enable minimization of the leakage of theretained electric charge in the direction of the film thickness or inthe transverse direction at the surface, which is caused by a loweringin the resistivity due to the adsorption of water, the influence ofmoisture, etc. In addition, since the glass transition temperature is100° C. or higher, fluorocarbon resins are superior in heat resistance.Therefore, the electric charge retaining performance is satisfactoryeven at high temperatures, and the stored electric charge only slightlychanges with time. Further, since fluorocarbon resins are soluble in afluorine-containing solvent, they are superior in processability. Inparticular, since coating is possible, these resins can be usedadvantageously to provide a uniform film thickness over a predeterminedarea or to obtain a thin film of several μm. On the other hand,polystyrene resins are superior in that the glass transition temperatureis high and the moisture absorption is low.

However, it has been revealed that fluorocarbon resins generally havelow positive electric charge retaining characteristics, although theyare excellent in negative electric charge (electron) retainingcharacteristics, and that when a polystyrene resin is used alone, highelectric charge retaining characteristics cannot be obtained. Thepresent inventors have found that, if fine particles of an insulatingorganic substance are dispersed in a fluorocarbon resin or a polystyreneresin, there is an improvement in electric charge retainingcharacteristics, particularly positive electric charge retainingperformance. Although the reason for this is not clear, it is consideredthat positive electric charge trap sites are produced at the interfacebetween the insulating organic substance fine particles and thefluorocarbon or polystyrene resin, which serves as a matrix, thus makingan improvement in the positive electric charge retaining performance.Accordingly, the electrostatic information recording medium of thepresent invention is improved in the performance of retainingelectrostatic information of not only negative electric charge but alsopositive electric charge. Therefore, it is possible to recordinformation independently of the kind of photosensitive member used forinformation recording.

A second electrostatic information recording medium of the presentinvention is characterized in that an electric charge retaining layer isstacked on at least an electrode layer, and that the electric chargeretaining layer comprises a fluorine-containing thermoplastic resin thatconsists of a repeating unit represented by formula (1): ##STR2## (wherethe content of the dioxonol component represented by the number m ofrepeating units is in the range of 20 mol % to 90 mol %, and where n isa positive integer)

the fluorine-containing thermoplastic resin having a melt viscosity of10² to 10⁴ Pa.sec at a temperature which is 90° C. to 110° C. higherthan its glass transition temperature.

We have found that the fluorine-containing thermoplastic resin of theabove formula (1) has a high resistivity, i.e., 1×10¹⁴ ohm-cm or higher,e.g., 10¹⁸ ohm-cm, excellent electric charge retaining performance and alow water absorption, i.e., 0.01% or lower, and hence enablesminimization of the leakage of the retained electric charge in thedirection of the film thickness or in the transverse direction at thesurface, which is caused by a lowering in the resistivity due toadsorption of water, and that since the glass transition temperature is100° C. or higher, the heat resistance is superior, and hence theelectric charge retaining performance is satisfactory even at hightemperatures, and the stored electric charge only slightly changes withtime. Thus, information electric charge can be stored for a long periodof time. Further, since the resin of the above formula (1) is soluble ina fluorine-containing solvent, it is superior in processability. Inparticular, since coating is possible, the resin can be usedadvantageously to provide a uniform film thickness over a predeterminedarea or to obtain a thin film of several μm.

A third electrostatic information recording medium of the presentinvention is characterized in that an electric charge retaining layer isstacked on at least an electrode layer, and that the electric chargeretaining layer comprises an insulating resin layer stacked on theelectrode layer, a photoconductive or electrically conductive fineparticle layer stacked on the insulating resin layer, and an insulatingresin layer stacked on the fine particle layer to a thickness of 0.1 μmto 1 μm, and further that the insulating resin is a fluorocarbon resin.

A method of producing the third electrostatic information recordingmedium according to the present invention is characterized in that afteran insulating resin layer has been formed on an electrode by coating,either a photoconductive fine particle layer or an electricallyconductive fine particle layer is formed on the insulating resin layerby vapor deposition under a low vacuum in a state where the insulatingresin layer does not soften, and another insulating resin layer isformed on the fine particle layer to a thickness of 0.1 μm to 1 μm bycoating, thereby producing an electrostatic information recordingmedium, and that the insulating resin is a fluorocarbon resin.

In the third electrostatic information recording medium of the presentinvention, an insulating resin layer having a thickness of 0.1 μm to 1μm has previously been stacked on either a photoconductive fine particlelayer or an electrically conductive fine particle layer. Therefore, itis surmised that the electrostatic charge that is formed on the surfaceof the insulating resin layer during electrostatic recording is causedto pass through the insulating resin layer by the action of an electricfield formed by the electrostatic charge and then retained in thephotoconductive or electrically conductive fine particles. Thus, theelectrostatic charge can be stably retained without the need to form aprotective film.

If the insulating resin layer is formed from a fluorocarbon resin, theresin layer has a high resistivity and a low water absorption, i.e.,0.01% or lower, and hence enables minimization of the leakage of theretained electric charge in the direction of the film thickness or inthe transverse direction at the surface, which is caused by a loweringin the resistivity due to adsorption of water. In addition, since theglass transition temperature is 100° C. or higher, the heat resistanceis superior, and hence the electric charge retaining performance issatisfactory even at high temperatures, and the stored electric chargeonly slightly changes with time. If the layer is formed by coating usinga solution prepared by dissolving a fluorocarbon resin in afluorine-containing solvent, superior processability is obtained, i.e.,it is possible to provide a uniform film thickness over a predeterminedarea or to obtain a thin film of several μm.

A fourth electrostatic information recording medium of the presentinvention is characterized in that an electric charge retaining layer isstacked on at least an electrode layer, and that the electric chargeretaining layer comprises an insulating resin layer formed from aninsulating organic substance having no photoconductivity and aninsulating resin, which is stacked on the electrode layer, aphotoconductive or electrically conductive fine particle layer stackedon the insulating resin layer, and another insulating resin layerstacked on the fine particle layer to a thickness of 0.1 μm to 1 μm, andfurther that the insulating resin is a fluorocarbon resin.

A method of producing the fourth electrostatic information recordingmedium according to the present invention is characterized in that afteran insulating resin layer having an insulating organic substance with nophotoconductivity dispersed therein has been formed on an electrode bycoating, either a photoconductive fine particle layer or an electricallyconductive fine particle layer is formed on the insulating resin layerby vapor deposition under a low vacuum in a state where the insulatingresin layer does not soften, and a fluorocarbon resin layer is formed onthe fine particle layer to a thickness of 0.1 μm to 1 μm by coating,thereby producing an electrostatic information recording medium.

In the fourth electrostatic information recording medium of the presentinvention, the insulating resin layer in the third electrostaticinformation recording medium is allowed to contain an insulating organicsubstance having no photoconductivity, thereby making it possible toimprove the negative electric charge retaining performance and,particularly, the positive electric charge retaining performance. Thus,it is possible to record information independently of the kind ofphotosensitive member used for information recording.

In addition, in the first to fourth electrostatic information recordingmediums of the present invention, the information electric charge storedtherein is extremely stable. Accordingly, these mediums can be used, forexample, as a recording drum for an ion flow printer. In such a case, itis possible to construct a so-called multi-printer in which after printinformation has been recorded by the ion flow printer, a desired numberof hard copies can be obtained. Further, the potential difference can bereadily detected by measuring the potential difference between theelectrode and the surface potential. In addition, it is possible tooutput an electric signal corresponding to the electrostatic latentimage and to display it on a CRT or to print it out by a sublimationtransfer printer or the like. Further, since the information storagemeans is arranged in units of electrostatic charge, the electrostaticinformation recording medium can store information of high quality andhigh resolution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are sectional views showing embodiments of the firstor second electrostatic information recording medium according to thepresent invention.

FIG. 2 is a schematic view showing an open-circuit thermally stimulatedcurrent measuring device used in the present invention.

FIG. 3 is a graph of a thermally stimulated current spectrum that isgenerally shown by the electrostatic information recording medium of thepresent invention.

FIG. 4 is a graph of a thermally stimulated current spectrum shown by anelectrostatic information recording medium wherein an insulating organicsubstance having no photoconductivity is not dispersed in its electriccharge retaining layer.

FIGS. 5(a) and 5(b) are sectional views showing embodiments of the thirdor fourth electrostatic information recording medium according to thepresent invention.

FIG. 6(a), 6(b), 6(c) and 6(d) illustrates a method of recordingelectrostatic information on the first to fourth electrostaticinformation recording mediums according to the present invention.

FIG. 7 illustrates one example of DC amplification type potentialreading method used to read the electrostatic information recorded onthe first to fourth electrostatic information recording mediumsaccording to the present invention.

FIG. 8 schematically illustrates an arrangement for a method ofreproducing the electrostatic information recorded on the first tofourth electrostatic information recording mediums according to thepresent invention.

FIG. 9 illustrates the arrangement of a multi-printer using theelectrostatic information recording medium of the present invention.

FIG. 10 is a graph showing the change of the positive electric chargeretaining rate with time in regard to an electrostatic informationrecording medium C having p-phenylenediamine dispersed in the electriccharge retaining layer in a case where it was stored under theconditions of 60° C. and 25% RH.

FIG. 11 is a graph showing thermally stimulated current spectra ofelectrostatic information recording mediums having p-phenylenediaminedispersed in their electric charge retaining layers.

FIG. 12 is a graph showing thermally stimulated current spectra ofelectrostatic information recording mediums having no organic substancefine particles dispersed in their electric charge retaining layers.

FIG. 13 is a graph showing a thermally stimulated current spectrum of anelectrostatic information recording medium having o-phenylenediaminedispersed in its electric charge retaining layer.

FIG. 14 is a graph showing a thermally stimulated current spectrum of anelectrostatic information recording medium having m-phenylenediaminedispersed in its electric charge retaining layer.

FIG. 15 is a graph showing the change of the electric charge retainingrate with time in regard to an electrostatic information recordingmedium W having 2,4,7-trinitrofluorenone dispersed in its electriccharge retaining layer in a case where it was stored under theconditions of 60° C. and 25% RH.

FIG. 16 is a graph showing the change of the electric charge retainingrate with time in regard to an electrostatic information recordingmedium having p-phenylenediamine added to its electric charge retaininglayer in a case where it was stored under the conditions of 60° C. and25% RH.

FIG. 17 is a graph showing the change of the electric charge retainingrate with time in regard to an electrostatic information recordingmedium having p-phenylenediamine added to its electric charge retaininglayer in a case where it was stored under the conditions of 40° C. and95% RH.

FIG. 18 is a graph showing the relationship between the electric chargeretaining rate and the p-phenylenediamine concentration in the electriccharge retaining layer in a case where electrostatic informationrecording mediums having p-phenylenediamine added to their electriccharge retaining layers were stored under the conditions of 60° C., 25%RH and 40° C., 95% RH.

FIG. 19 is a graph showing the change of the electric charge retainingrate with time in regard to an electrostatic information recordingmedium having phenothiazine added to its electric charge retaining layerin a case where it was stored under the conditions of 60° C. and 25% RH.

FIG. 20 is a graph showing the change of the electric charge retainingrate with time in regard to an electrostatic information recordingmedium having phenothiazine added to its electric charge retaining layerin a case where it was stored under the conditions of 40° C. and 95% RH.

FIG. 21 is a graph showing the change of the electric charge retainingrate with time in regard to an electrostatic information recordingmedium having trinitrofluorenone added to its electric charge retaininglayer in a case where it was stored under the conditions of 60° C. and25% RH.

FIG. 22 is a graph showing the change of the electric charge retainingrate with time in regard to an electrostatic information recordingmedium having trinitrofluorenone added to its electric charge retaininglayer in a case where it was stored under the conditions of 40° C. and95% RH.

FIG. 23 is a graph showing the relationship between the electric chargeretaining rate and the trinitrofluorenone concentration in the electriccharge retaining layer in a case where an electrostatic informationrecording medium having trinitrofluorenone added to its electric chargeretaining layer was stored under the conditions of 60° C., 25% RH and40° C., 95% RH.

FIG. 24 is a graph for explanation of the relationship between thethickness of an insulating resin layer as the outermost surface layerand the electric charge retaining performance.

BEST MODE FOR CARRYING OUT THE INVENTION

First of all, the first electrostatic information recording medium willbe described.

FIGS. 1(a) and 1(b) are sectional views showing embodiments of the firstelectrostatic information recording medium. In the figure, referencenumeral 3 denotes an electrostatic information recording medium, 11 anelectric charge retaining layer, 13 an electrode, and 15 a substrate.

As a fluorocarbon resin, a fluorocarbon resin of high insulationquality, which has a resistivity of 10¹⁴ ohm-cm or higher, is used.Examples of usable resins include fluorocarbon resins such aspoly(tetrafluoroethylene) (PTFE), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylenecopolymer (FEP), tetrafluoroethylene-hexafluoropropylene-perfluoroalkylvinyl ether copolymer (EPE), tetrafluoroethylene-ethylene copolymer(ETFE), poly(chlorotrifluoroethylene) (PCTFE),chlorotrifluoroethylene-ethylene copolymer (ECTFE), pentafluorostyrenepolymer, etc. It is also possible to use thermoplastic resins,thermosetting resins, energy radiation curing resins such as ultravioletcuring resins, electron radiation curing resins, engineering plastics,etc., in which a part or all the hydrogen atoms have been replaced byfluorine atoms.

Further, it is possible to use a fluorine-containing thermoplastic resinconsisting of a repeating unit of a ring structure represented by theformula: ##STR3## and/or the formula: ##STR4## (where n is 1 or 2) thefluorine-containing thermoplastic resin having such a molecular weightthat the intrinsic viscosity at 50° C. is at least 0.1, and afluorine-containing thermoplastic resin consisting of a repeating unit(a) of a ring structure represented by the formula: ##STR5## and/or theformula: ##STR6## (where n is 1 or 2) and a repeating unit (b)represented by the formula:

    --(CF.sub.2 --CFX)--

(where X is F, Cl, --O--CF₂ CF₂ CF₃, --O--CF₂ CF(CF₃)OCF₂ CF₂ SO₃ F, or--O--CF₂ CF₂ CF₂ COOCH₃)

the fluorine-containing thermoplastic resin containing at least 80% byweight of repeating unit (a) and having an intrinsic viscosity of atleast 0.1 at 50° C.

The repeating unit (a) is obtained by radical cyclopolymerization of aperfluoroaryl vinyl ether or perfluorobutenyl vinyl ether represented bythe formula:

    CF.sub.2 ═CF--O--(CF.sub.2).sub.n CF═CF.sub.2

(where n is 1 or 2)

A fluorine-containing thermoplastic resin that contains both therepeating units (a) and (b) is obtained by radical polymerization of aperfluorovinyl ether represented by the formula:

    CF.sub.2 ═CF--O--(CF.sub.2).sub.n CF═CF.sub.2

(where n is 1 or 2)

and a monomer represented by the formula:

    CF.sub.2 ═CFX

(where X is F, Cl, --O--CF₂ CF₂ CF₃, --O--CF₂ CF(CF₃)OCF₂ CF₂ SO₃ F, or--O--CF₂ CF₂ CF₂ COOCH₃)

These resins are disclosed, for example, in Japanese Patent ApplicationLaid-Open (KOKAI) No. 1-131215.

Further, it is possible to use a fluorine-containing thermoplastic resinthat consists of a repeating unit represented by ##STR7## (where thecontent of the dioxonol component represented by the number m ofrepeating units is in the range of 20 mol % to 90 mol %)

the fluorine-containing thermoplastic resin having a melt viscosity of10² to 10⁴ Pa.sec at a temperature which is 90° C. to 110° C. higherthan its glass transition temperature.

Specific examples of fluorine-containing thermoplastic resinsrepresented by the above formula (1) are "Teflon" AF1600 (trade name),manufactured by Du Pont Co., Ltd., containing about 65 mol % dioxonolunit and having a glass transition temperature of 160° C., a meltviscosity of 2657 Pa.sec (measured by ASTM D3835 at 250° C. and 100sec⁻¹) and a water absorption of 0.01% or less, and "Teflon" AF2400(trade name), manufactured by Du Pont Co., Ltd., containing about 85 mol% dioxonol unit and having a glass transition temperature of 240° C., amelt viscosity of 540 Pa.sec (measured by ASTM D3835 at 350° C. and 100sec-⁻¹) and a water absorption of 0.01% or less.

Next, an organic substance that is to be dispersed in the fluorocarbonresin must exhibit no photoconductivity and have insulation quality of10⁶ ohm-cm or higher in terms of resistivity and further needs to beinsoluble in a fluorine-containing solvent, which is used as a solventfor the above-described fluorocarbon resin, but dispersible in thefluorocarbon resin. Further, it is preferable for the organic substanceto have a boiling temperature higher than the heat-treating temperaturein a drying process carried out during the production of anelectrostatic information recording medium so that the organic substancewill not evaporate during the drying process.

There is no specific restriction on such an organic substance, providedthat the above-described requirements are satisfied. Examples of such anorganic substance include benzenes and naphthalenes having at least onegroup selected from among amino, nitro and halogen groups as asubstituent, cyclohexanes having a halogen group as a substituent,polymers such as polymethacrylic acid, and photosensitizers such as2,4,7-trinitrofluorenone, 7,7,8,8-tetracyanoquinodimethane,phenothiazine, perylene, phthalic anhydride, maleic anhydride,fluorenyl, triphenylamine, etc. The organic substance is preferablycontained in the fluorocarbon resin in an amount of 10⁻⁴ wt % to 1 wt %.If the amount of organic substance dispersed in the fluorocarbon resinis less than 10⁻⁴ wt %, the addition of the organic substance producesno effect. If the amount of organic substance exceeds 1 wt %, it becomesdifficult to disperse the substance, and the effectiveness obtained bythe addition of the organic substance lessens.

It is preferable that the above-described organic substances bedispersed by using glass beads or the like in a solution prepared bydissolving a fluorocarbon resin in a fluorine-containing solvent, e.g.,Florinato FC-40, FC-75, etc. (trade name; manufactured by 3M (K.K.)).

The dispersion may be coated on the electrode layer by a method, forexample, spinner coating, spraying, brushing, dipping, etc. After thecoating process, the fluorine-containing solvent is removed byevaporation at a temperature higher than the boiling point of thesolvent, and then the coating is dried. In this way, it is possible toobtain an electric charge retaining layer having a thickness of 0.1 μmto 100 μm, preferably 0.1 μm to 10 μm. If the thickness is less than 0.1μm, the electric charge. retained in the layer may leak, whereas, if thethickness exceeds 100 μm, the electrostatic information recording mediumwill lose the required flexibility.

It should be noted that the dispersion may be formed into a film andbonded to the electrode through an adhesive or the like. It is alsopossible to stack an electrode forming material on one side of afluorocarbon resin film by vapor deposition or other similar method.However, it is preferable to produce the electric charge retaining layerby coating from the viewpoint of processability.

Next, as a polystyrene resin, one which has insulation quality of about10¹⁶ ohm-cm in terms of resistivity and a molecular weight of 10³ to 10⁶is generally used. If the molecular weight is less than 10³ or exceeds10⁶, the coatability and the film stability are unfavorable. Examples ofsuch polystyrene resins include Piccolastic D125, A75, D75, D125, D137,D150, etc. (trade name; manufactured by Rika Hercules Co.). Examples ofsolvents usable for these polystyrene resins are xylene, toluene,monochlorobenzene, methyl ethyl ketone, chloroform, benzene,tetrahydrofuran, etc.

Any of the organic substances which may be added to the above-describedfluorocarbon resin can similarly be used as an organic substance to beadded to the polystyrene resin. The method of stacking the polystyreneresin layer on the electrode and the layer thickness are the same asthose in a case where the above-described fluorocarbon resin is used.

When thermally stimulated currents in the electric charge retaininglayer are measured, a spectrum representing the relationship between theheating temperature and the thermally stimulated current is obtained. Inthe case of the first electrostatic information recording medium of thepresent invention, the spectrum has not only an ordinary homo-peak butalso a hetero-peak which does not appear when an electric chargeretaining layer is formed from a fluorocarbon resin alone, although thereason for this is not clear.

FIG. 2 is a schematic view showing an open-circuit TSC (ThermallyStimulated Current measuring device (manufactured by (K.K.) Toyo SeikiSeisakusho) used to measure thermally stimulated currents. Theopen-circuit TSC measuring device is arranged as follows: Anelectrically charged sample 1 that is provided on an electrode 2 isdisposed to face an upper electrode 3 at a predetermined distance. Thetwo electrodes are connected together with an ammeter 4 interposedtherebetween. With this arrangement, currents are measured while thesample is being heated at a predetermined rate of temperature rise.

The measurement is effected in such a way that changes in the potentialof the upper electrode induced by the surface potential of theelectrically charged sample are taken out in the form of current changesin an external circuit. Normally, the sign of the current taken out isopposite to the sign of the surface potential of the sample. That is, ifthe surface potential is positive, the thermally stimulated current isnegative, whereas, if the. surface potential is negative, the thermallystimulated current is positive. The current having the normal sign isreferred to as "homo-current", while the current having the signopposite to the normal is referred to as "hetero-current". In theelectrostatic information recording medium of the present invention,when a thermally stimulated current spectrum, which represents therelationship between the heating temperature and the induced current, ismeasured with the heating temperature changed, the spectrum has ahetero-peak in addition to an ordinary homo-peak. It should be notedthat, when the electric charge retaining layer is negatively charged, nohetero-peak appears.

FIG. 3 shows schematically a thermally stimulated current spectrum whichis generally shown by the electrostatic information recording medium ofthe present invention. FIG. 4 shows schematically a thermally stimulatedcurrent spectrum measured in a case where an insulating organicsubstance having no photoconductivity is not dispersed in the electriccharge retaining layer. As shown in FIG. 3, the electrostaticinformation recording medium of the present invention shows ahetero-peak (b) in addition to an ordinary homo-peak (a). However, inFIG. 4, only negative currents flow, and no hetero-current flows.

Next, the second electrostatic information recording medium of thepresent invention will be described.

In the second electrostatic information recording medium, the electriccharge retaining layer in the above-described first electrostaticinformation recording medium is replaced by an electric charge retaininglayer which is formed on the electrode by using singly afluorine-containing thermoplastic resin of the above formula (1), shownon page 6, and by employing the same stacking method as in the case ofthe first electrostatic information recording medium.

The electric charge retaining layer of the electrostatic informationrecording medium may contain photoconductive or electrically conductivefine particles in order to enhance the electric charge storing function.

Examples of usable photoconductive fine particle materials are inorganicphotoconductive materials such as amorphous silicon, crystallinesilicon, amorphous selenium, crystalline selenium, cadmium sulfide, zincoxide, etc., and organic photoconductive materials such aspolyvinylcarbazole, phthalocyanine, azo pigment, etc.

Examples of usable electrically conductive materials are elements of thefollowing groups in the periodic table: the group 1A (alkali metals),the group 1B (copper group), the group 2A (alkaline earth metals), thegroup 2B (zinc group), the group 3A (aluminum group), the group 3B (rareearth elements), the group 4B (titanium group), the group 5B (vanadiumgroup), the group 6B (chromium group), the group 7B (manganese group),the group 8 (iron group and platinum group), group 4A (carbon group)elements, i.e., carbon, silicon, germanium, tin and lead, group 5A(nitrogen group) elements, i.e., antimony and bismuth, and group 6A(oxygen group) elements, i.e., sulfur, selenium and tellurium. Thesematerials are used in the form of fine powder. Among the above-describedelements, the metals may also be used in the form of metal ions or fineparticles of alloys, organic metal compounds or complexes. Further, theabove-described elements may be used in the form of oxides, phosphides,sulfides or halides. Carbon, gold, copper, and aluminum are preferablyused.

To allow the fine particles to be present in the electric chargeretaining layer, first, the resin of formula (1) is dissolved in afluorocarbon resin system solvent mentioned in the description of thefirst electrostatic information recording medium, and a resin layer isformed under the same coating conditions, thereby forming an electriccharge retaining layer. Thereafter, the resin layer is heated to theregion of the softening point thereof, and the above-described fineparticle forming material is deposited by using a low-pressuredeposition apparatus at a low pressure of about 10 Torr to 10⁻³ Torr.Consequently, the fine particle forming material condenses in the formof ultrafine particles having a diameter of about 10 μm to 0.1 μm. Inthis way, the fine particles can be made present in the vicinity of thesurface of the resin layer.

The fine particle material may be dispersed in an amount in the range offrom 10⁻⁴ wt % to 1 wt % in a resin solution prepared by using afluorine-containing solvent mentioned in the description of the firstelectrostatic information recording medium, and formed on the electrodeby using a coating method and stacking conditions (film thickness, etc.)as mentioned in the description of the first electrostatic informationrecording medium.

Next, the third and fourth electrostatic information recording mediumsof the present invention will be described.

FIGS. 5(a) and 5(b) are sectional views showing embodiments of the thirdand fourth electrostatic information recording mediums according to thepresent invention. In the figure, reference numeral 3 denotes anelectrostatic information recording medium, 10 an insulating resinlayer, 11 a photoconductive or electrically conductive fine particlelayer, 12 an insulating resin layer having a thickness of 0.1 μm to 1μm, 13 an electrode, and 15 a substrate.

A resin that is used to form the insulating resin layers 10 and 12 isrequired to have insulation quality of at least 10¹⁴ ohm-cm in terms ofresistivity in order to suppress the migration of information electriccharge. A resin that is used to form an electric charge retaining layerneeds to have a glass transition temperature higher than the servicetemperature from the viewpoint of electric charge retaining performance.Examples of usable resins include thermoplastic resins, thermosettingresins, energy radiation curing resins such as ultraviolet curing resinsand electron radiation curing resins, and engineering plastics. Thefluorocarbon resins mentioned for the first electrostatic informationrecording medium are particularly preferably used.

For the fourth electrostatic information recording medium also, any ofthe organic substances having no photoconductivity mentioned for thefirst electrostatic information recording medium is usable in the sameway.

First, to form the insulating resin layer 10, it is preferable to usethe resin solution and coat it by the same method as in the case of theelectric charge retaining layer in the first electrostatic informationrecording medium. Further, a photoconductive fine particle layer orelectrically conductive fine particle layer 11 is provided on theinsulating resin layer 10. For the photoconductive or electricallyconductive fine particle layer 11, the photoconductive or electricallyconductive fine particle materials mentioned in the description of thesecond electrostatic information recording medium can be used.

The fine particle layer 11 is stacked on the insulating resin layer byvapor deposition using a low-pressure deposition apparatus at atemperature lower than the melting temperature of the resin of theinsulating resin layer. When evaporated at a low pressure of about 10Torr to 10⁻³ Torr, the deposition material condenses in the form ofultrafine particles having a diameter of about 0.1 μm to 10 μm, whichare stacked in the form of a single layer or a plurality of alignedlayers on the insulating resin layer. Then, the insulating resin layer12 is coated on the fine particle layer to a thickness of 0.1 μm to 1 μmby the same method as in the formation of the insulating resin layer 10.

The information recording mechanism in the third and fourthelectrostatic information recording mediums is considered to be asfollows. When electric charge is formed on the surface of theelectrostatic information recording medium by electrostatic recording,the surface electric charge is caused to pass through the insulatingresin layer 12 by the action of an electric field formed by the surfaceelectric charge and the electric charge of the opposite polarity inducedin the electrode by the surface electric charge, and stably retained inthe photoconductive or electrically conductive fine particles. If thethickness of the layer 12 exceeds 1 μm, the surface electric chargecannot pass therethrough but merely remains in the form of surfaceelectric charge. Accordingly, no electric charge is injected into thefine particles. Therefore, a layer thickness exceeding 1 μm is notpreferable. The insulating resin layer 12 makes it unnecessary to form aprotective layer after recording. Thus, it is possible to realize anelectrostatic information recording medium improved in electric chargeretaining performance.

In production of the electrostatic information recording medium, a fineparticle layer is deposited on the insulating resin layer 10 held at atemperature lower than the softening point thereof. Therefore, it ispossible to use resins having a relatively high softening point inaddition to the resins mentioned for the second electrostaticinformation recording medium. Accordingly, it is possible to widen therange of selection of resins used as a material for forming the resinlayer. It should be noted that, if a fluorocarbon resin is used as aninsulating resin, even more excellent electric charge retainingperformance is achieved by virtue of the high insulation quality and lowwater absorption of the fluorocarbon resin.

As has been described above, the first to fourth electrostaticinformation recording mediums of the present invention are designed torecord information in the electric charge retaining layer or the fineparticle layer in the form of a distribution of electrostatic charges.Accordingly, the electrostatic information recording medium may beformed in various shapes in accordance with the kind of information tobe recorded or the recording method employed. For example, when theelectrostatic information recording medium is used for a camera, it isformed in the shape of ordinary film (for a single frame or for a seriesof frames), a disk or a card. When digital or analog information is tobe recorded thereon by laser or the like, the electrostatic informationrecording medium is formed in the shape of a tape, a disk or a card.

The substrate 15 in FIGS. 1 and 5 is employed to support theelectrostatic information recording medium. Accordingly, there are nospecific restrictions on the thickness and material of the substrate,provided that it is sufficiently strong to support the electric chargeretaining layer. Examples of usable materials are a flexible plasticfilm, metal foil, paper, or a rigid material such as glass, plasticsheet, metal sheet (capable of serving also as an electrode), etc. Thereare cases where the substrate 15 needs to be capable of transmittinglight. In such cases, if necessary, anti-reflection properties can begiven by providing a layer having anti-reflection effect, or adjustingthe film thickness to a level at which anti-reflection effect isobtainable, or combining these two. When the electrostatic informationrecording medium is formed in the shape of a flexible film, tape, diskor card, a flexible plastic film is used as the substrate. When theelectrostatic information recording medium is required to have a certainlevel of strength, a rigid sheet or inorganic material, for example,glass, is used as the substrate.

The electrode 13 in FIGS. 1 and 5 may be formed on the substrate 15.There is no restriction on the material of the electrode 13, providedthat the specific resistance of the material is not higher than 10⁶ohm-cm. Examples of such material are an inorganic metallic conductivefilm, e.g., zinc, titanium, copper, iron, tin, etc., an inorganicmetallic oxide conductive film, e.g., tin oxide, indium oxide, zincoxide, titanium oxide, tungsten oxide, vanadium oxide, etc., and anorganic conductive film, e.g., quaternary ammonium salt, and so forth.These materials may be used alone or in the form of a composite materialcomprising two or more of them. Among these materials, oxidesemiconductors are preferable; indium-tin oxide is particularlypreferable. Such an electrode is formed on the substrate by vapordeposition, sputtering, CVD, coating, plating, dipping, electrolyticpolymerization or the like. The layer thickness of the electrode needsto be changed depending upon the electrical characteristics of thematerial thereof and the level of voltage applied to record information.For example, the thickness is about from 100 Å to 3,000 Å. The electrode13 may be formed either on the whole area between the substrate and theelectric charge retaining layer or in conformity with the pattern of theelectric charge retaining layer formed.

The electrostatic information recording mediums shown in FIGS. 1(b) and5(b) have no substrate 15. These electrostatic information recordingmediums are produced in such a manner that after an electric chargeretaining layer has been formed in the shape of a film, an electrodelayer is formed on a surface of the electric charge retaining layer byvapor deposition, laminating, etc. In the third or fourth electrostaticinformation recording medium, the electrode layer is provided on thesurface of the electric charge retaining layer which is reverse to theside where the fine particle layer is stacked.

The surface of the first or second electrostatic information recordingmedium of the present invention is preferably formed with a protectivefilm after recording of information to protect the surface againstdamage and to prevent decay of the stored information electric charge.As a protective film, a plastic film may be used. Alternatively, aprotective film may be formed by coating of a plastic solution or byvapor deposition or the like to a thickness of from several hundreds Åto several tens μm. In this order of thickness, the stored informationcan be reproduced without hindrance.

When the electrostatic information recording medium needs to be endowedwith photosensitivity at the same time, the electric charge retaininglayer in the first or second electrostatic information recording mediumof the present invention should be stacked by coating or bonding on thesurface of a photoconductive layer of a photosensitive member having thephotoconductive layer on an electrode. In the case of the electriccharge retaining layer in the third or fourth electrostatic informationrecording medium, it should be stacked at the side thereof where thefine particle layer is provided.

The following is a description of a method of recording electrostaticinformation on the first to fourth electrostatic information recordingmediums and a method of reproducing the recorded information therefrom.FIGS. 6(a), 6(b), 6(c) and 6(d) are views for explanation of theelectrostatic information recording method. In the figure, referencenumeral 1 denotes a photosensitive member, 3 an electrostaticinformation recording medium, 5 a substrate, 7 an electrode, 9 aphotoconductive layer, 17 a power supply, and 19 information light.

First, a transparent electrode 7 of ITO having a thickness of 1,000 Å isformed on a substrate 5 of glass having a thickness of 1 mm, and aphotoconductive layer 9 having a thickness of about 10 μm is formedthereon to form a photosensitive member 1. As shown in FIG. 6(a), theelectrostatic information recording medium 3 is disposed face-to-facewith the photosensitive member 1 across an air gap of about 10 μm.

Next, a voltage is applied between the electrodes 7 and 13 from thepower supply 17, as shown in FIG. 6(b). Although in the figure thevoltage is applied in such a manner that the photosensitive member sideis positive, while the electrostatic information recording medium isnegative, when negative electric charge information is to be recorded onthe electrostatic information recording medium, the photosensitivemember side must be negative.

If the photosensitive member 1 and the electrostatic informationrecording medium 3 are placed in the dark, since the photoconductivelayer 9 is a highly resistive element, no change occurs between theelectrodes as long as the voltage applied across the air gap is lowerthan the discharge initiating voltage according to Paschen's law. When avoltage that exceeds the discharge initiating voltage is applied acrossthe air gap from an external power supply, an electric discharge isinduced, so that electric charge is stored on the electrostaticinformation recording medium. This state continues until the appliedvoltage lowers down to the discharge initiating voltage, thus formingbackground electric charge. When light 18 is applied from thephotosensitive member (1) side, regions of the photoconductive layer 9where the light is incident become electrically conductive, inducing anelectric discharge, and thus allowing electric charge to be stored onthe electrostatic information recording medium. In a case where uniformbackground electric charge has been provided in advance, electric chargeis further stored in the regions where the light is incident. Then, thepower supply 17 is turned off, and the electrostatic informationrecording medium 3 is separated from the photosensitive member 1, thuscompleting the formation of an electrostatic latent image. When planaranalog recording is effected by this electrostatic information recordingmethod, a high resolution is obtained in the same way as in the silverhalide photography, and the recorded information can be stored for along period of time without decay of the electric charge.

As a method of inputting information to the electrostatic informationrecording medium of the present invention, a method using ahigh-resolution electrostatic camera or a recording method using lasermay be employed. The high-resolution electrostatic camera that is usedin the present invention employs the electrostatic information recordingmedium of the present invention in place of a photographic film used inordinary cameras. The electrostatic information recording medium isplaced in close contact or face-to-face with a photosensitive member,and with a voltage being applied to the two electrodes, an electrostaticlatent image is formed in accordance with the incident optical image.Either an optical or electric shutter can be used for this camera. It isalso possible to conduct color photography by using a color filter bywhich light information is separated into R, G and B light componentsand taken out in the form of parallel rays through prisms, and formingone frame from the electrostatic information recording medium separatedinto R, G and B light components or from one set of R, G and B imagesarranged on one plane.

In the recording method by laser, argon laser (514 nm, 488 nm),helium-neon laser (633 nm) or semiconductor laser (780 nm, 810 nm, etc.)may be used as a light source. The photosensitive member and theelectrostatic information recording medium are brought into closecontact with each other at their surfaces or they are placed so as toface each other at a predetermined distance, and a voltage is appliedthereto. In this case, it is preferable to set the photosensitive memberelectrode so as to have the same polarity as that of carriers in thephotosensitive member. Under such conditions, laser exposurecorresponding to a picture image signal, character signal, code signalor line drawing signal is performed by scanning. Analog recording suchas that of a picture image is effected by modulating the intensity oflaser light, whereas digital recording such as that of characters, codeor line drawing is effected by on/off control of laser light. A pictureimage consisting of halftone dots is formed by on/off controlling laserlight through a dot generator. It should be noted that thephotoconductive layer in the photosensitive member need not havepanchromatic spectral characteristics, but it is only required to havesensitivity to the wavelength of the laser light source employed.

Recording of information on the electrostatic information recordingmedium of the present invention can also be effected by an electrostaticrecording method that employs an electrode stylus head or an ion flowhead, or a recording method that employs an optical printer, e.g., alaser printer, or a recording method that employs an electron beam, ionimplantation, etc. instead of using the above-described photosensitivemember.

The method of reproducing the electrostatic information recorded on theelectrostatic information recording medium will next be explained. FIG.7 shows an example of an electric potential reading method in theelectrostatic information recording and reproducing method, in which thesame reference numerals as those shown in FIGS. 1(a) and 1(b) denote thesame contents. In this figure, reference numeral 21 denotes an electricpotential reading unit, 23 a detection electrode, 25 a guard electrode,27 a capacitor, and 29 a voltmeter.

To reproduce the information electric charge stored on the electrostaticinformation recording medium, first, the electric potential reading unit21 is placed face-to-face with the surface of the electrostaticinformation recording medium. Consequently, an electric field that isgenerated by the electric charge stored in the fine particle layer actson the detection electrode 23, and electric charge equivalent to theelectric charge on the electrostatic information recording medium isinduced on the surface of the detection electrode 23. Since thecapacitor 27 is charged with electric charge equivalent in quantity butopposite in polarity to the induced charge, a potential differenceaccording to the stored electric charge is produced between theelectrodes of the capacitor. By reading this value with the voltmeter29, the electric potential of the information electric charge can beobtained. By scanning the surface of the electrostatic informationrecording medium with the electric potential reading unit 21, anelectrostatic latent image can be output in the form of an electricsignal. It should be noted that, when the detection electrode 23 aloneis used, the resolution may be reduced by the action of an electricfield (electric lines of force) produced by the electric charge in awider range than the region of the electrostatic information recordingmedium which faces the detection electrode. Therefore, a guard electrode25 which is grounded may be disposed around the detection electrode.Thus, the electric lines of force are directed to extend perpendicularlyto the plane, so that the electric lines of force only in the regionfacing the detection electrode 23 act. This makes it possible to readthe electric potential at a region which has approximately the same areaas that of the detection electrode. Because the accuracy and resolutionof the potential reading greatly depend upon the shape and size of thedetection electrode and the guard electrode, together with the distancefrom the electrostatic information recording medium, it is essential todesign on the basis of optimal conditions obtained in conformity withthe required performance. The potential may also be read optically bythe photoelectric effect using a material having an electrooptic effect,for example, an optical crystal, e.g., LiNbO₃, or an organic opticalmaterial, e.g., a liquid crystal.

FIG. 8 schematically shows an arrangement which may be employed to carryout the electrostatic information reproducing method. In the figure,reference numeral 31 denotes an electric potential reading unit, 33 anamplifier, 35 a CRT, and 37 a printer.

Referring to the figure, the electric charge potential is detected withthe electric potential reading unit 31, and the detected output isamplified in the amplifier 33 and displayed on the CRT 35. It can alsobe printed out from the printer 37. In this case, it is possible toselect any portion which is desired to read and to output the readelectric potential at any desired time. It is also possible to reproducethe information repeatedly. In addition, it is also possible to readoptically by use of a material whose optical properties change with theelectric field, for example, an electrooptic crystal. Since theelectrostatic latent image can be obtained in the form of an electricsignal, it can also be utilized for, for example, recording onto anotherrecording medium, if necessary.

The electrostatic information, e.g., characters, images, etc., recordedon the electrostatic information recording medium of the presentinvention can be stored semipermanently without decaying practically.Accordingly, if the electrostatic information recording medium is used,for example, as a recording drum for an ion flow printer, it is possibleto construct a so-called multi-printer in which recording of printinformation is carried out only once by the ion flow printer and adesired number of hard copies can be obtained thereafter. FIG. 9 showsone example of the multi-printer. In the figure, reference numeral 3denotes a drum-shaped electrostatic information recording medium, 41electrostatic charge, 42 toner, 43 an ion head, 44 a transfer means, 45a toner developing device, and 46 transfer paper.

As shown in the figure, while the electrostatic information recordingmedium 3 of the present invention, which is formed in the shape of adrum, is being rotated, the ion head 43 is driven on the basis of signalinformation or the like to give the electrostatic information recordingmedium electrostatic charge 41 corresponding to the information, andthen the electrostatic charge is developed with toner. Thereafter, thetoner is transferred to the transfer paper 56 electrostatically or byfusing, thereby enabling a hard copy to be obtained. Since theelectrostatic information recording medium of the present invention issuperior in the electric charge retaining performance, a desired numberof hard copies can be obtained by driving the ion head 43 only once onthe basis of signal information or the like.

The present invention will be described below by way of examples. Itshould be noted that in the following description Examples 1 to 13 areconcerned with the first electrostatic information recording medium,while Examples 14 to 17 are concerned with the second electrostaticinformation recording medium, and Example 18 and those following itrelate to the third or fourth electrostatic information recordingmedium.

(EXAMPLE 1)

1.2 mg of o-phenylenediamine, 2.6 g of fluorocarbon resin (Cytop, tradename, manufactured by Asahi Glass Company, Ltd.), and 50 g ofperfluoro-(2-butyltetrahydrofuran) as a solvent were put in a mayonnaisebottle, and glass beads No. 1 were added thereto until the volumethereof accounted for about 80%. Then, the mayonnaise bottle was shakenfor 12 hours with a shaker (Red Devil), thereby preparing an organicsubstance fine particle dispersion.

The dispersion was coated on an ITO transparent electrode (thickness:about 500 Å; resistance: 80 ohm/sq.) by a spin coater (600 rpm; 20 sec)and air-dried for 1 hour and then dried for 1 hour in an oven at 150°C., thereby obtaining an electrostatic information recording medium Ahaving a film thickness of 2.4 μm.

Electrostatic information recording mediums B and C were prepared in thesame manner as the above by using m-phenylenediamine andp-phenylenediamine, respectively, in place of the o-phenylenediamine inthe electrostatic information recording medium A.

The surface of the electric charge retaining layer in each electrostaticinformation recording medium was charged by a corona charger so that thesurface potential was +100 V for one sample and -100 V for another.Thereafter, each electrostatic information recording medium was allowedto stand for 30 days under three different test conditions:

(1) indoor conditions (ordinary temperature and humidity);

(2) accelerated test conditions of 60° C. and 25% RH; and

(3) accelerated test conditions of 40° C. and 95% RH.

Thereafter, electric charge retaining performance was measured for eachof the test conditions. The results are shown in Table below.

    ______________________________________                                                After standing                                                                for 30 days                                                                   under indoor                                                          Electrostatic                                                                         conditions                                                            information                                                                           (ordinary  After standing                                                                             After standing                                recording                                                                             temperature &                                                                            for 30 days at                                                                             for 30 days at                                medium  humidity)  60° C. & 25% RH                                                                     40° C. & 95% RH                        ______________________________________                                        A       ±95 V   +85 V:-90 V  ±95 V                                      B       ±95 V   +85 V:-90 V  ±95 V                                      C       ±95 V   +85 V:-90 V  ±95 V                                      ______________________________________                                    

FIG. 10 shows the change of the positive electric charge retaining ratewith time in regard to the electrostatic information recording medium Chaving p-phenylenediamine dispersed therein in a case where it wasstored under the conditions of 60° C. and 25% RH. In the figure, represents the electrostatic information recording medium C, and ∘represents an electrostatic information recording medium prepared in thesame way as the electrostatic information recording medium C except thatno p-phenylenediamine was added thereto.

It will be understood from the figure that the electrostatic informationrecording medium C having p-phenylenediamine dispersed therein hasexcellent electric charge retaining characteristics even underhigh-temperature conditions in comparison to the electrostaticinformation recording medium prepared without adding p-phenylenediaminethereto.

Further, electrostatic information recording mediums havingp-phenylenediamine dispersed therein were prepared in the same way asthe above except that the thickness of the electric charge retaininglayer was about 2 μm. Then, the respective electric charge retaininglayers of the electrostatic information recording mediums prepared weresubjected to corona charging so that surface potentials of +320 V (a),+160 V (b), +80 V (c) and +40 V (d) were set up, respectively. Then, theelectric charge retaining layer of each electrostatic informationrecording medium was raised in temperature from 20° C. to 220° C., andthermally stimulated currents were measured during the rise intemperature.

The results of the measurement are shown in FIG. 11. In the meantime,the electrostatic information recording mediums were negatively charged,and thermally stimulated currents were measured in the same way as theabove. However, no hetero-current was induced.

Further, electrostatic information recording mediums were prepared inthe same way as the above except that no organic substance fineparticles were dispersed therein, and positively charged in the same wayas the above. Then, thermally stimulated currents were measured in thesame way as the above. The results of the measurement are shown in FIG.12. In the figure, a represents an electrostatic information recordingmedium having an initial potential of +40 V, b another medium having aninitial potential of +100 V, and c still another medium having aninitial potential of +200 V.

As will be understood from the figures, when an electrostaticinformation recording medium having an organic substance fine particlesdispersed therein is positively charged, a hetero-peak appears in thethermally stimulated current spectrum thereof.

FIG. 13 shows the results of measurement of thermally stimulatedcurrents in the electrostatic information recording medium A charged sothat the surface potential was +80 V. FIG. 14 shows the results ofmeasurement of thermally stimulated currents in the electrostaticinformation recording medium B charged so that the surface potential was+100 V. In these cases, the thermally stimulated currents were measuredin the same way as the above.

(EXAMPLE 2)

1.2 mg of p-phenylenediamine, 2.6 g of fluorocarbon resin (TeflonAF1600, trade name, manufactured by Du Pont Co., Ltd.), and 50 g ofFlorinato FC-40 (trade name, manufactured by 3M (K.K.)) as a solventwere put in a mayonnaise bottle, and glass beads No. 1 were addedthereto until the volume thereof accounted for 80%. Then, the mayonnaisebottle was shaken for 12 hours with a shaker (Red Devil), therebypreparing an organic substance fine particle dispersion.

By using this dispersion, an electrostatic information recording mediumwas prepared in the same way as in Example 1, and the electric chargeretaining performance of the medium was measured in the same way as inExample 1.

After the electrostatic information recording medium had been allowed tostand for 30 days at 60° C. and 25% RH, the surface electric charge wasmeasured. As a result, it was revealed that the electrostaticinformation recording medium had surface potentials of +50 V and -85 V,which proves that both positive electric charge and negative electriccharge can satisfactorily be retained.

Thermally stimulated currents in this electrostatic informationrecording medium were measured in the same way as in Example 1. As aresult, it was confirmed that the thermally stimulated current spectrumhad a hetero-peak similar to the above.

(EXAMPLE 3)

Electrostatic information recording mediums D, E and F were prepared inthe same manner as in Example 1 by using 1.75 mg of1,5-diaminonaphthalene, 1,8-diaminonaphthalene, and2,3-diaminonaphthalene, respectively, in place of the o-phenylenediaminein Example 1, and the electric charge retaining performance of eachmedium was measured in the same way as in Example 1.

After the electrostatic information recording mediums had been allowedto stand for 30 days at 60° C. and 25% RH, the surface electric chargewas measured for each medium. As a result, it was revealed that theelectrostatic information recording medium D had surface potentials of+71 V and -90 V, while the electrostatic information recording medium Ehad surface potentials of +90 V and -90 V, and the electrostaticinformation recording medium F had surface potentials of +60 V and -90V. Thus, it has been proved that both positive electric charge andnegative electric charge can satisfactorily be retained.

Thermally stimulated currents in the electrostatic information recordingmediums D, E and F were measured in the same way as in Example 1. As aresult, it was confirmed that the thermally stimulated current spectrahad a hetero-peak similar to the above.

(EXAMPLE 4)

Electrostatic information recording mediums G and H were prepared in thesame manner as in Example 1 by using 1.85 mg of o-dinitrobenzene andm-dinitrobenzene, respectively, in place of the o-phenylenediamine inExample 1, and the electric charge retaining performance of each mediumwas measured in the same way as in Example 1.

After the electrostatic information recording mediums had been allowedto stand for 30 days at 60° C. and 25% RH, the surface electric chargewas measured for each medium. As a result, it was revealed that theelectrostatic information recording medium G had surface potentials of+80 V and -90 V, and the electrostatic information recording medium Halso had surface potentials of +80 V and -90 V. Thus, it has been provedthat both positive electric charge and negative electric charge cansatisfactorily be retained.

Thermally stimulated currents in the electrostatic information recordingmediums G and H were measured in the same way as in Example 1. As aresult, it was confirmed that the thermally stimulated current spectrahad a hetero-peak similar to the above.

(EXAMPLE 5)

Electrostatic information recording mediums I, J, K, L and M wereprepared in the same manner as in Example 1 by using 1.6 mg ofp-dichlorobenzene, 2.0 mg of 1,2,3-trichlorobenzene, 2.0 mg of1,2,4-trichlorobenzene, 2.0 mg of 1,3,5-trichlorobenzene, and 3.15 mg of1,2,3,4,5,6-hexachlorobenzene, respectively, in place of theo-phenylenediamine in Example 1, and the electric charge retainingperformance of each medium was measured in the same way as in Example 1.

After the electrostatic information recording mediums had been allowedto stand for 30 days at 60° C. and 25% RH, the surface electric chargewas measured for each medium. As a result, it was revealed that theelectrostatic information recording medium I had surface potentials of+75 V and -90 V; the electrostatic information recording medium J hadsurface potentials of +75 V and -90 V; the electrostatic informationrecording medium K had surface potentials of +75 V and -90 V; theelectrostatic information recording medium L had surface potentials of+75 V and -90 V; and the electrostatic information recording medium Mhad surface potentials of +70 V and -90 V. Thus, it has been proved thatboth positive electric charge and negative electric charge cansatisfactorily be retained.

Thermally stimulated currents in the electrostatic information recordingmediums I, J, K, L and M were measured in the same way as in Example 1.As a result, it was confirmed that the thermally stimulated currentspectra had a hetero-peak similar to the above.

(EXAMPLE 6)

Electrostatic information recording mediums N, O, P, Q, R and S wereprepared in the same manner as in Example 1 by using 1.5 mg of1-nitroaniline, 1.5 mg of 2-nitroaniline, 1.5 mg of 3-nitroaniline, 1.7mg of 1-amino-3-nitroaniline, 1.7 mg of 1-amino-2-nitroaniline, and 1.7mg of 1-nitro-2-aminoaniline, respectively, in place of theo-phenylenediamine in Example 1, and the electric charge retainingperformance of each medium was measured in the same way as in Example 1.

After the electrostatic information recording mediums had been allowedto stand for 30 days at 60° C. and 25% RH, the surface electric chargewas measured for each medium. As a result, it was revealed that theelectrostatic information recording medium N had surface potentials of+30 V and -90 V; the electrostatic information recording medium O hadsurface potentials of +30 V and -90 V; the electrostatic informationrecording medium P had surface potentials of +30 V and -90 V; theelectrostatic information recording medium Q had surface potentials of+80 V and -90 V; the electrostatic information recording medium R hadsurface potentials of +85 V and -90 V; and the electrostatic informationrecording medium S had surface potentials of +85 V and -90 V. Thus, ithas been proved that both positive electric charge and negative electriccharge can satisfactorily be retained.

Thermally stimulated currents in the electrostatic information recordingmediums N, O, P, Q, R and S were measured in the same way as inExample 1. As a result, it was confirmed that the thermally stimulatedcurrent spectra had a hetero-peak similar to the above.

(EXAMPLE 7)

Electrostatic information recording mediums T, U and V were prepared inthe same manner as in Example 1 by using 1.2 mg of polymethylmethacrylate fine particles (MP1451, MP-1000 and MP-1600, trade name,manufactured by Soken Kagaku-sha) having primary particle diameterdistributions of 0.1 μm to 0.2 μm, 0.35 μm to 0.5 μm, and 0.6 μm to 0.9μm, respectively, in place of the o-phenylenediamine in Example 1, andthe electric charge retaining performance of each medium was measured inthe same way as in Example 1.

After the electrostatic information recording mediums had been allowedto stand for 30 days at 60° C. and 25% RH, the surface electric chargewas measured for each medium. As a result, it was revealed that theelectrostatic information recording medium T had surface potentials of+46 V and -85 V; the electrostatic information recording medium U hadsurface potentials of +45 V and -86 V; and the electrostatic informationrecording medium V had surface potentials of +38 V and -85 V. Thus, ithas been proved that both positive electric charge and negative electriccharge can satisfactorily be retained, and that the smaller the particlediameter, the more excellent in the positive electric charge retainingperformance.

Thermally stimulated currents in the electrostatic information recordingmediums T, U and V were measured in the same way as in Example 1. As aresult, it was confirmed that the thermally stimulated current spectrahad a hetero-peak similar to the above.

(EXAMPLE 8)

Electrostatic information recording mediums W, X, Y, Z. a, b, c and dwere prepared in the same manner as in Example 1 by using 3.5 mg of2,4,7-trinitrofluorenone, 2.25 mg of 7,7,8,8-tetracyanoquinodimethane,2.2 mg of phenothiazine, 2.8 mg of perylene, 1.6 mg of phthalicanhydride, 2.0 mg of fluorenyl, 2.7 mg of triphenylmethane, and 1.1 mgof maleic anhydride, respectively, in place of the o-phenylenediamine inExample 1, and the electric charge retaining performance of each mediumwas measured in the same way as in Example 1.

After the electrostatic information recording mediums had been allowedto stand for 30 days at 60° C. and 25% RH, the surface electric chargewas measured for each medium. As a result, it was revealed that theelectrostatic information recording medium W had surface potentials of+75 V and -90 V; the electrostatic information recording medium X hadsurface potentials of +73 V and -91 V; the electrostatic informationrecording medium Y had surface potentials of +72 V and -82 V; theelectrostatic information recording medium Z had surface potentials of+70 V and -82 V; the electrostatic information recording medium a hadsurface potentials of +57 V and -82 V; the electrostatic informationrecording medium b had surface potentials of +73 V and -91 V; theelectrostatic information recording medium c had surface potentials of+50 V and -65 V; and the electrostatic information recording medium dhad surface potentials of +43 V and -78 V. Thus, it has been proved thatboth positive electric charge and negative electric charge cansatisfactorily be retained.

FIG. 15 shows the change of the electric charge retaining rate with timein regard to the electrostatic information recording medium W having2,4,7-trinitrofluorenone dispersed therein in a case where it was storedunder the conditions of 60° C. and 25% RH. In the figure, □ representsthe electrostatic information recording medium W, and ▪ represents anelectrostatic information recording medium prepared in the same way asthe electrostatic information recording medium W except that no2,4,7-trinitrofluorenone was dispersed therein.

It will be understood from the figure that the electrostatic informationrecording medium W having 2,4,7-trinitrofluorenone dispersed therein hasexcellent electric charge retaining characteristics even under thehigh-temperature conditions in comparison to the electrostaticinformation recording medium having no 2,4,7-trinitrofluorenonedispersed therein.

Thermally stimulated currents in the electrostatic information recordingmediums W, X, Y, Z. a, b, c, and d were measured in the same way as inExample 1. As a result, it was confirmed that the thermally stimulatedcurrent spectra had a hetero-peak similar to the above.

(EXAMPLE 9)

(Method of Preparation of Single-Layer Organic Photosensitive Member)

A mixture having a composition consisting essentially of 10 g ofpoly-N-vinylcarbazole (manufactured by Anan Koryo (K.K.)), 10 g of2,4,7-trinitrofluorenone, 2 g of polyester resin (binder: Byron 200;manufactured by Toyo Spinning Co., Ltd.), and 90 g of tetrahydrofuran(THF) was prepared in the dark and applied by using a doctor blade to aglass substrate (1 mm thick) having In₂ O₃ --SnO₂ deposited thereon to athickness of about 1,000 Å by sputtering, and then subjected tothrough-flow drying for about 1 hour at 60° C., thereby obtaining aphotosensitive member having a photoconductive layer with a thickness ofabout 10 μm. The photosensitive member was further dried naturally for 1day in order to dry it completely.

(Electrostatic Information Recording and Reproducing Method)

The photosensitive member prepared above and the electrostaticinformation recording medium having p-phenylenediamine dispersedtherein, prepared in Example 1, were placed face-to-face with each otheracross a spacer comprising a polyester film having a thickness of 10 μmso that the surface of the electrostatic information recording mediumand the photoconductive layer side of the photosensitive member facedeach other and grounded. Then, a DC voltage of ±600 V was appliedbetween the two electrodes.

With the voltage being applied in this way, exposure was carried out for1 second from the photosensitive member side with a 1,000 lux halogenlamp used as a light source, thus completing formation of anelectrostatic latent image.

Then, the potential difference between the electrode and the surface ofthe medium was measured. As a result, surface potentials of +80 V and-80 V were measured at the surface of the medium with a surfacepotential measuring device, while the surface potential at the unexposedregion was ±10 V.

After the electrostatic information recording medium had been allowed tostand for 30 days at 60° C. and 25% RH, the surface electric charge wasmeasured. As a result, it was revealed that the electrostaticinformation recording medium had surface potentials of +75 V and -75 V.Thus, it is proved that both positive electric charge and negativeelectric charge can satisfactorily be retained.

(EXAMPLE 10)

0.0195 g of p-phenylenediamine was dissolved in 20 g of a mixed solventcomprising Piccolastic D125 (trade name, manufactured by Rika HerculesCo.) and xylene in the ratio of 3:7 to prepare a 0.33 wt % solution.

This solution was coated on an ITO transparent electrode (filmthickness: about 500 Å; and resistance: 80 ohm/sq.) by using a spincoater (1000 rpm; 20 sec) and then dried for 1 hour in an oven at 100°C. to obtain an electrostatic information recording medium having athickness of 5 μm.

The surface of the electric charge retaining layer in the electrostaticinformation recording medium was charged by a corona charger so that thesurface potential was +180 V for one sample and -180 V for another.Thereafter, the electric charge retaining performance was measured underthe high-temperature conditions of 60° C. and 25% RH as an acceleratedtest. The results of the measurement are shown in FIG. 16.

Further, the electric charge retaining performance under thehigh-humidity conditions of 40° C. and 95% RH was measured. The resultsof the measurement are shown in FIG. 17.

In the meantime, electrostatic information recording mediums wereprepared in the same way as the above except that solutions respectivelyhaving organic substance concentrations of 3.3 wt % and 0.1 wt % wereused, and then charged. One day after the charging process, the electriccharge retaining performance of each medium was measured in the same wayas the above. The results of the measurement are shown in FIG. 18.

It will be understood from the figure that the electrostatic informationrecording medium of the present invention is superior in the electriccharge retaining performance, particularly in the positive electriccharge retaining performance, and that the electric charge retainingperformance improves as the organic substance concentration rises.

(EXAMPLE 11)

0.0179 mg of phenothiazine was dissolved in 20 g of a mixed solventcomprising Piccolastic D125 (trade name, manufactured by Rika HerculesCo.) and xylene in the ratio of 3:7 to prepare a 0.3 wt % solution. Byusing this solution, an electrostatic information recording medium wasobtained under the same conditions as in Example 10.

The surface of the electric charge retaining layer in the electrostaticinformation recording medium was charged by a corona charger so that thesurface potential was +170 V for one sample and -170 V for another.Thereafter, the electric charge retaining performance was measured underthe high-temperature conditions of 60° C. and 25% RH as an acceleratedtest. The results of the measurement are shown in FIG. 19.

Further, the electric charge retaining performance under thehigh-humidity conditions of 40° C. and 95% RH was measured. The resultsof the measurement are shown in FIG. 20.

(EXAMPLE 12)

0.0284 mg of 2,4,7-trinitro-9-fluorenone was dissolved in 20 g of amixed solvent comprising Piccolastic D125 (trade name, manufactured byRika Hercules Co.) and xylene in the ratio of 3:7 to prepare a 0.47 wt %solution. By using this solution, an electrostatic information recordingmedium was obtained under the same conditions as in Example 10.

The surface of the electric charge retaining layer in the electrostaticinformation recording medium was charged by a corona charger so that thesurface potential was +170 V for one sample and -170 V for another.Thereafter, the electric charge retaining performance was measured underthe high-temperature conditions of 60° C. and 25% RH as an acceleratedtest. The results of the measurement are shown in FIG. 21.

Further, the electric charge retaining performance under thehigh-humidity conditions of 40° C. and 95% RH was measured. The resultsof the measurement are shown in FIG. 22.

In the meantime, electrostatic information recording mediums wereprepared in the same way as the above except that solutions respectivelyhaving organic substance concentrations of 0% (no organic substanceadded), 0.0047 wt %, 0.0094 wt % and 0.047 wt % were used, and thencharged. One day after the charging process, the electric chargeretaining performance of each medium was measured in the same way as theabove. The results of the measurement are shown in FIG. 23.

It will be understood from the figure that the electrostatic informationrecording medium of the present invention is superior in the electriccharge retaining performance, particularly in the positive electriccharge retaining performance, and that the electric charge retainingperformance improves as the organic substance concentration rises.

(EXAMPLE 13)

(Electrostatic Information Recording and Reproducing Method)

The photosensitive member prepared in Example 9 and the electrostaticinformation recording medium having 0.33 wt % of p-phenylenediaminedispersed in the electric charge retaining layer, prepared in Example10, were placed face-to-face with each other across a spacer comprisinga polyester film having a thickness of 10 μm so that the surface of theelectrostatic information recording medium and the photoconductive layerside of the photosensitive member faced each other and grounded. Then, aDC voltage of ±600 V was applied between the two electrodes.

With the voltage being applied in this way, exposure was carried out for1 second from the photosensitive member side with a 1,000 lux halogenlamp used as a light source, thus completing formation of anelectrostatic latent image.

Then, the potential difference between the electrode and the surface ofthe medium was measured. As a result, surface potentials of +100 V and-100 V were measured at the surface of the medium with a surfacepotential measuring device, while the surface potential at the unexposedregion was ±10 V.

After the electrostatic information recording medium had been allowed tostand for 30 days under ordinary temperature and humidity conditions,the surface electric charge was measured. As a result, it was revealedthat the electrostatic information recording medium had surfacepotentials of +90 V and -80 V, and that the electric charge,particularly the positive electric charge was satisfactorily retained.

Examples of the second electrostatic information recording medium willbe shown below.

(EXAMPLE 14)

A fluorine-containing resin (Teflon AF1600, trade name, manufactured byDu Pont Co., Ltd.; water absorption: not higher than 0.01%; resistivity:1×10¹⁸ ohm-cm) was dissolved in perfluoro-(2-butyltetrahydrofuran) toobtain a 5% solution. This solution was coated on an ITO (indium-tinoxide) transparent electrode (thickness: 500 Å; resistance: 80 ohm/sq.)by spin coating (1000 rpm; 20 sec), air-dried for 1 hour and then driedfor 1 hour in an oven at 200° C., thereby forming an electric chargeretaining layer having a dry film thickness of 3 μm.

The surface of the electric charge retaining layer thus obtained wascharged by a corona charger so that the surface potential was -120 V,and the electric charge retaining performance thereof was measured.

In an accelerated test where the surface potential of the electriccharge retaining layer was measured after the electrostatic informationrecording medium had been allowed to stand for 30 days under theconditions of 60° C. and 25% RH, it was revealed that the electriccharge retaining layer still maintained a residual potential of -91 V.

When the surface potential of the electric charge retaining layer wasmeasured after the electrostatic information recording medium had beenallowed to stand for 30 days at 40° C. and 95% RH, it was revealed thatthe electric charge retaining layer still maintained a residualpotential of -104 V.

(EXAMPLE 15)

The surface of the electric charge retaining layer in the electrostaticinformation recording medium prepared in Example 14 was charged by acorona charger so that the surface potential was +120 V, and theelectric charge retaining performance was measured.

In an accelerated test where the surface potential of the electriccharge retaining layer was measured after the electrostatic informationrecording medium had been allowed to stand for 1 day under theconditions of 60° C. and 25% RH, it was revealed that the electriccharge retaining layer still maintained a residual potential of ±16 V.After the electrostatic information recording medium had been allowed tostand for 30 days under the same conditions, a residual potential of +5V was still maintained.

When the surface potential of the electric charge retaining layer wasmeasured after the electrostatic information recording medium had beenallowed to stand for 1 day under the conditions of 40° C. and 95% RH,the electric charge retaining layer still maintained a residualpotential of +29 V. After the electrostatic information recording mediumhad been allowed to stand for 30 days under the same condition, aresidual potential of +11 V was still maintained.

(EXAMPLE 16)

On a glass substrate having a thickness of 1 mm, an Al electrode wasstacked to a thickness of 1,000 Å by vacuum deposition method (10⁻⁵Torr). The surface of the Al electrode was coated by a blade coater witha solution of 5% a fluorine-containing resin (Teflon AF1600, trade name,manufactured by Du Pont Co., Ltd.; water absorption: not higher than0.01%; resistivity: 1×10¹⁸ ohm-cm) inperfluoro-(2-butyltetrahydrofuran), thereby producing an electric chargeretaining layer having a dry film thickness of 3 μm.

The surface of the electric charge retaining layer was charged by acorona charger so that the surface potential was -100 V, and theelectric charge retaining performance thereof was measured.

After the electrostatic information recording medium had been allowed tostand for 30 days under ordinary temperature and humidity conditions thesurface potential of the electric charge retaining layer was measured.As a result, it was revealed that the electric charge retaining layerstill maintained a residual potential of -85 V. After the electrostaticinformation recording medium had been allowed to stand for 30 days at60° C. and 25% RH as an accelerated test, the electric charge retaininglayer still maintained a residual potential of -70 V. In an acceleratedtest where the electrostatic information recording medium was allowed tostand for 30 days at 40° C. and 95% RH, it was revealed that a residualpotential of -80 V was still maintained.

(EXAMPLE 17)

(Electrostatic Information Recording and Reproducing Method)

The photosensitive member prepared in Example 9 and the electrostaticinformation recording medium prepared in Example 14 were placedface-to-face with each other across a spacer comprising a polyester filmhaving a thickness of 10 μm so that the surface of the electrostaticinformation recording medium and the photoconductive layer side of thephotosensitive member faced each other and grounded. Then, a DC voltageof -700 V was applied between the two electrodes in such a manner thatthe photosensitive member side was negative, while the electrostaticinformation recording medium side was positive.

With the voltage being applied in this way, exposure was carried out for1 second from the photosensitive member side with a 1,000 lux halogenlamp used as a light source, thus completing formation of anelectrostatic latent image.

Then, the potential difference between the electrode and the surface ofthe medium was measured. As a result, surface potential of -100 V wasmeasured at the surface of the medium with a surface potential measuringdevice, while the surface potential at the unexposed region was -30 V.The medium that was subjected to exposure and voltage application byusing a gray scale in the same way as the above had a surface potentialpattern recorded thereon in analog form in the range of from -30 V to-100 V.

Even after the medium had been allowed to stand for 1 year at roomtemperature, substantially the same surface potential was maintained.

Next, Examples of the third or fourth electrostatic informationrecording medium will be shown below.

(EXAMPLE 18)

On a glass substrate having a thickness of 1 mm, indium-tin oxide (ITO;thickness: about 500 Å; resistance: 80 ohm/sq.) was stacked. The surfaceof the electrode was coated by spinner coating method (1000 rpm; 20 sec)with a solution of 7% a fluorocarbon resin (Cytop, trade name,manufactured by Asahi Glass Company, Ltd.) in a fluorine-containingsolvent perfluoro-(2-butyltetrahydrofuran)!, thereby forming a resinlayer having a dry film thickness of 2.9 μm.

With the above used as a substrate, selenium was deposited thereon for10 minutes at a substrate heating temperature of 45° C. under a lowvacuum (6 torr) so that the average particle diameter was not largerthan 0.5 μm.

Further, the surface of the deposition layer was coated with theabove-described fluorocarbon resin solution by spinner coating method sothat the dry film thickness was 0.6 μm. In this way, variouselectrostatic information recording mediums were produced.

Next, the surface of the medium was charged in the dark by coronacharging so that the surface potential was +120 V (-120 V), and thenlight was applied thereto. Consequently, the potential became +115 V(-115 V). Thus, internal electric charge was formed.

Even after this medium had been allowed to stand for 30 days under thehigh-temperature conditions of 60° C. and 20% RH as an accelerated test,it still retained a potential of +50 V (-100 V). Even after it had beenallowed to stand for 30 days under the high-humidity conditions of 40°C. and 95% RH, the medium still maintained +50 V (-100 V).

Next, electrostatic information recording mediums which were differentfrom each other in the thickness of the outermost fluorocarbon resinlayer were prepared in the same way as the above and charged so that thesurface potential was -120 V. Thereafter, light was applied thereto toform internal electric charge. The electric charge retaining rate wasmeasured for each of the mediums after they had been allowed to standfor 1 day under the high-temperature conditions of 60° C. and 20% RH.

The results of the measurement are shown in FIG. 24. It will beunderstood that the electric charge retaining rate reaches a maximumvalue when the thickness of the outermost fluorocarbon resin layer is0.6 μm.

(EXAMPLE 19)

An electrostatic information recording medium was prepared in the sameway as in Example 18 except that tellurium was used as a depositionmaterial in place of selenium and deposited for 7 minutes at a substrateheating temperature of 50° C. and a degree of vacuum of 3 torr, therebyforming a fine particle layer having an average particle diameter of notlarger than 0.5 μm.

The surface of this medium was charged by corona charging so that thesurface potential was +120 V (-120 V). Thereafter, the medium wasallowed to stand for 30 days under the high-temperature conditions of60° C. and 20% RH. Even after standing under such conditions, the mediumstill maintained a potential of +50 V (-100 V). Even after the mediumhad been allowed to stand for 30 days under the high-humidity conditionsof 40° C. and 95% RH, it still maintained a surface potential of +50 V(-100 V).

(EXAMPLE 20)

An electrostatic information recording medium was prepared in the sameway as in Example 18 except that zinc was used as a deposition materialin place of selenium and deposited for 5 minutes at a substrate heatingtemperature of 50° C. to 60° C. and a degree of vacuum of 0.1 torr,thereby forming a fine particle layer having an average particlediameter of not larger than 0.5 μm.

The surface of this medium was charged by corona charging so that thesurface potential was +120 V (-120 V). Thereafter, the medium wasallowed to stand for 30 days under the high-temperature conditions of60° C. and 20% RH. Even after standing under such conditions, the mediumstill maintained a potential of +90 V (-100 V). Even after the mediumhad been allowed to stand for 30 days under the high-humidity conditionsof 40° C. and 95% RH, it still maintained a surface potential of +85 V(-100 V).

(EXAMPLE 21)

An electrostatic information recording medium A was prepared in the sameway as in Example 18 except that a dispersion, which was obtained byputting 1.2 mg of o-phenylenediamine, 2.6 g of fluorocarbon resin(Cytop, trade name, manufactured by Asahi Glass Company, Ltd.) and 50 gof perfluoro-(2-butyltetrahydrofuran) as a solvent in a mayonnaisebottle, adding glass beads No. 1 thereto until the volume thereofaccounted for about 80%, and shaking the mayonnaise bottle for 12 hourswith a shaker (Red Devil), was used as a fluorocarbon resin solution.

Electrostatic information recording mediums B and C were prepared in thesame manner as the above by using m-phenylenediamine andp-phenylenediamine, respectively, in place of the o-phenylenediamine inthe electrostatic information recording medium A.

The surface of the electric charge retaining layer in each electrostaticinformation recording medium was charged by a corona charger so that thesurface potential was +120 V for one sample and -120 V for another.Thereafter, each electrostatic information recording medium was allowedto stand for 30 days under the conditions of 60° C. and 25% RH as anaccelerated test, and then the electric charge retaining performance wasmeasured. As a result, it was revealed that all the electrostaticinformation recording mediums A, B and C had surface potentials of +50 Vand -100 V, and that these electrostatic information recording mediumswere also superior in the positive electric charge retainingperformance.

(EXAMPLE 22)

1.2 mg of o-phenylenediamine, 2.6 g of fluorocarbon resin (TeflonAF1600, trade name, manufactured by Du Pont Co., Ltd.), and 50 g ofFlorinato FC-40 (trade name, manufactured by 3M (K.K.)) as a solventwere put in a mayonnaise bottle, and glass beads No. 1 were addedthereto until the volume thereof accounted for 80%. Then, the mayonnaisebottle was shaken for 12 hours with a shaker (Red Devil), therebypreparing an organic substance fine particle dispersion.

By using this dispersion, an electrostatic information recording mediumwas prepared in the same way as in Example 18, and the electric chargeretaining performance thereof was measured in the same way as in Example18.

After the electrostatic information recording medium had been allowed tostand for 30 days at 60° C. and 20% RH, the surface electric chargethereof was measured. As a result, it was revealed that the medium hadsurface potentials of +50 V and -100 V. Thus, it has been proved thatboth positive electric charge and negative electric charge cansatisfactorily be retained.

(EXAMPLE 23)

An electrostatic information recording medium was prepared in the sameway as in Example 18 except that an aluminum-deposited polyethyleneterephthalate film (thickness: 20 μm) was used in place of the glassprovided with the fluorocarbon resin-coated ITO electrode.

The surface of this medium was charged by corona charging so that thesurface potential was +800 V for one sample and -800 V for another. Whenthe surface potential was measured after the medium had been allowed tostand for 90 days at 60° C. and 20% RH, it was revealed that the mediumstill maintained surface potentials of +580 V and -750 V.

(EXAMPLE 24)

(Electrostatic Information Recording and Reproducing Method)

The photosensitive member prepared in Example 9 and the electrostaticinformation recording medium prepared in Example 18 were placedface-to-face with each other across a spacer comprising a polyester filmhaving a thickness of 10 μm so that the surface of the electrostaticinformation recording medium and the photoconductive layer side of thephotosensitive member faced each other and grounded. Then, a DC voltageof ±600 V was applied between the two electrodes.

With the voltage being applied in this way, exposure was carried out for1 second from the photosensitive member side with a 1,000 lux halogenlamp used as a light source, thus completing formation of anelectrostatic latent image.

Then, the potential difference between the electrode and the surface ofthe medium was measured. As a result, surface potentials of +80 V and-80 V were measured at the surface of the medium with a surfacepotential measuring device, while the surface potential at the unexposedregion was ±10 V.

After the electrostatic information recording medium had been allowed tostand for 30 days at 60° C. and 20% RH, the surface potential wasmeasured. As a result, it was revealed that the electrostaticinformation recording medium had surface potentials of +35 V and -70 V,and that both the positive electric charge and negative electric chargewere satisfactorily retained.

(Comparative Example 1)

On a glass substrate having a thickness of 1 mm, ITO was stacked, and a7% solution of a fluorocarbon resin (Cytop, trade name, manufactured byAsahi Glass Company, Ltd.) in a fluorine-containing solvent was coatedon the electrode by spinner coating method (1000 rpm; 20 sec) so thatthe dry film thickness was 2.9 μm.

Next, the surface of this medium was charged by corona charging so thatthe surface potential was +100 V for one sample and -100 V for another.Thereafter, the medium was allowed to stand for 30 days under thehigh-temperature conditions of 60° C. and 20% RH. As a result, thepotential became +10 V and -100 V. After the medium was allowed to standfor 30 days under the high-humidity conditions of 40° C. and 95% RH, thepotential became +20 V and -100 V.

(Comparative Example 2)

On ITO stacked on a glass substrate having a thickness of 1 mm, a 50%solution of a thermoplastic resin (Stebelite ester 10, trade name,manufactured by Rika Hercules Co.; softening point: 71° C. to 78° C.) inmonochlorobenzene was coated by spin coating method (2000 rpm; 20 sec)so that the dry film thickness was 5 μm.

Next, the glass substrate was heated to 70° C. by a heater plate, and inthis state, selenium was deposited thereon for about 15 minutes under alow vacuum (6 torr), thereby providing an a-selenium particle layerhaving an average particle diameter of 0.5 μm near the surface of thethermoplastic resin layer, and thus obtaining an electrostaticinformation recording medium.

The surface of this electrostatic information recording medium wascharged in the dark by corona charging so that the surface potential was+200 V for one sample and -200 V for another, and then light was appliedthereto to form surface potentials of +180 V and -180 V as internalelectric charge. Thereafter, the electric charge retaining performancethereof was measured.

When the surface potential was measured after the medium had beenallowed to stand for 10 days under ordinary temperature and humidityconditions, the surface potentials of the two samples were +30 V and -50V, respectively.

(Comparative Example 3)

On ITO stacked on a glass substrate having a thickness of 1 mm, a 30%solution of a thermoplastic polystyrene resin (Piccolastic D125, tradename, manufactured by Rika Hercules Co.; softening point: 125° C.) inxylene was coated by spin coating method (1000 rpm; 20 sec) so that thedry film thickness was 5 μm. Next, the glass substrate was heated to110° C. by a heater plate, and in this state, selenium was depositedthereon for about 15 minutes under a low vacuum (6 torr), therebyproviding an a-selenium particle layer having an average particlediameter of 0.5 μm near the surface of the thermoplastic resin layer,and thus obtaining an electrostatic information recording medium.

The surface of this electrostatic information recording medium wascharged in the dark by corona charging so that the surface potential was+200 V for one sample and -200 V for another, and then light was appliedthereto to form surface potentials of +180 V and -180 V as internalelectric charge. Thereafter, the electric charge retaining performancethereof was measured.

When the surface potential was measured after the medium had beenallowed to stand for 10 days under ordinary temperature and humidityconditions, the surface potentials of the two samples were +30 V and -65V, respectively. When the medium was allowed to stand for 10 days underthe high-temperature conditions of 60° C. and 20% RH as an acceleratedtest, the surface potentials of the two samples became +10 V and -15 V,respectively.

Comparative Example 4)

An electrostatic information recording medium was prepared in the sameway as in Example 18 except that no fluorocarbon resin was provided onthe deposition layer, and the electric charge retaining performance ofthis medium was measured in the same way as in Example 18.

When the medium was allowed to stand for 30 days under thehigh-temperature conditions of 60° C. and 20% RH, the surface potentialsof the two samples became +40 V and -75 V, respectively. When the mediumwas allowed to stand for 30 days under the high-humidity conditions of40° C. and 95% RH, the surface potentials of the two samples became +30V and -70 V, respectively.

Industrial Applicability

The electrostatic information recording medium of the present inventionhas improved negative electric charge retaining performance and isparticularly superior in the positive electric charge retainingperformance. Accordingly, it is possible to record informationindependently of the kind of photosensitive member used. In addition,the information electric charge stored therein is extremely stable.Further, since the information storage means is arranged in units ofelectrostatic charge, the electrostatic information recording medium canstore information of high quality and high resolution. It is thereforepossible to output an electric signal corresponding to the storedinformation electric charge and to display it on a CRT or to print itout by a sublimation transfer printer or the like. In addition, theelectrostatic information recording medium of the present invention canbe used, for example, as a recording drum for an ion flow printer. Insuch a case, it is possible to construct a so-called multi-printer whichenables a desired number of hard copies to be obtained.

What is claimed is:
 1. An electrostatic information recording mediumhaving an electric charge retaining layer stacked on at least anelectrode layer, wherein said electric charge retaining layer comprisesa fluorine-containing thermoplastic resin consisting of a repeating unitrepresented by formula (1) ##STR8## (where the content of the dioxonolcomponent represented by the number m of repeating units is in the rangeof 20 mol % to 90 mol %, and where n is a positive integer)said fluorinecontaining thermoplastic resin having a melt viscosity of 10² to 10⁴Pa.sec at a temperature which is 90° C. to 110° C. higher than its glasstransition temperature.
 2. An electrostatic information recording mediumhaving an electric charge retaining layer stacked on at least anelectrode layer, wherein said electric charge retaining layer comprisesan insulating resin layer stacked on said electrode layer, aphotoconductive or electrically conductive fine particle layer stackedon said insulating resin layer, and an insulating resin layer stacked onsaid fine particle layer to a thickness of 0.1 μm to 1 μm, wherein atleast one of said insulating resin layers is a fluorocarbon having aresistivity of at least 10¹⁴ ohm-cm.
 3. An electrostatic informationrecording medium according to claim 2, wherein said insulating resin isa fluorocarbon resin.
 4. An electrostatic information recording mediumaccording to claim 2, wherein at least one of said insulating resinlayers has water absorption characteristics at least sufficient tosubstantially reduce migration of information electric charge.
 5. Amethod of producing an electrostatic information recording medium,wherein after an insulating resin layer has been coated on an electrode,either a photoconductive fine particle layer or an electricallyconductive fine particle layer is formed on said insulating resin layerby vapor deposition under a low vacuum in a state where said insulatinglayer is coated on said fine particle layer to a thickness of 0.1 μm to1 μm, wherein said insulating resin layer is a fluorocarbon having aresistivity of at least 10¹⁴ ohm-cm.
 6. An electrostatic informationrecording medium producing method according to claim 5, wherein saidinsulating resin is a fluorocarbon resin.
 7. A method of producing anelectrostatic information recording medium according to claim 5, whereinsaid insulating resin layer has water absorption characteristics atleast sufficient to substantially reduce migration of informationelectric charge.